Oil reservoirs are used, for example, in motor vehicle technology for storing the oil of a hydrostatic fan system circulated in a circuit through the reservoir for cooling the engine. According to the prior art, such oil reservoirs are frequently not equipped with an oil filter. However, since abraded particles or possible impurities must be filtered out of the oil in order to protect the components of the hydraulic system, an appropriate oil filter must be disposed in a different location of the system when using an oil reservoir without integrated oil filter.
However, oil reservoirs having an integrated oil filter that is disposed inside the oil reservoir are also known. Such an oil reservoir is described, for example, in DE 199 25 635 A1. In the case of the oil reservoir described in this document, the oil filter accommodated in the oil reservoir is further encapsulated in a separate filter housing inside the oil reservoir housing. Due to the special design, the oil filter is disposed completely beneath the oil level independently of the fill level otherwise present in the oil reservoir, so that the oil cannot pick up any air during filtration, which can impair the functionality of the cooling system and, as a result, may cause units in the motor vehicle to fail. Admittedly, an oil reservoir designed according to this document makes the separate arrangement of an oil filter in the hydraulic system outside of the oil reservoir expendable, and additionally effectively prevents impairments of the system due to air present in the oil. With respect to the necessary encapsulation of the oil filter inside the oil reservoir, however, the solution is comparatively complex.
Another possibility to avoid impairment of the cooling system due to air present in the oil in the form of air bubbles is to dispose guide devices in the oil reservoir for the directed oil guidance. Such guide devices lengthen the otherwise relatively short distance between the oil inlet fitting and the oil outlet fitting or fittings and promote a separation of air that may be present in the oil on this extended distance, wherein in addition the effectiveness of this measure is decisively determined by the geometry of the guide devices and the guidance track they set for the oil. In this respect, cyclone systems have been successfully applied for separating the air, such as those described in EP 1 669 119 A1 and U.S. Pat. No. 6,348,087 B1, for example. By way of such cyclone systems, the oil, together with any air bubbles that may be present therein, is caused to rotate on a circular track, and the air is thereby separated from the oil due to the developing centrifugal force and the different densities between the hydraulic fluid and air. While in this context in particular EP 1 669 119 A1 also relates to the configuration of an appropriate cyclone arrangement inside or as part of an oil reservoir, the oil reservoir according to the publication relates to a reservoir without an integrated oil filter. When used inside an oil reservoir, the solution known from the U.S. patent is also obviously not intended to be combined with an oil filter.